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Can someone point me at a guide on performance monitoring and capacity management of an Apache web farm? Other questions suggest some tools, but I'm also interested in understanding what the various performance parameters are, how to tweak them, tradeoffs among the configuration settings etc.

The web farm is mostly a reverse proxy for a weblogic tier, using the weblogic wlproxy for load balancing across the weblogic servers. It terminates SSL connections, but otherwise does very little other than pass things to and from weblogic. A (hardware) loadbalancer fronts the web servers.

I have already seen this :)

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closed as not constructive by mgorven, Tom O'Connor, Tim Brigham, mdpc, Mark Henderson Feb 20 '13 at 4:39

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See:… – gparent Feb 19 '13 at 19:36
See also:… – gparent Feb 19 '13 at 19:37
Yes. I'd seen both of those. I could perhaps have been clearer - this is a site already in operation and load-testing isn't going to be possible. I want to retrofit some decent monitoring, understand when limits are getting close, and what to do about them. SO more about day-to-day actions than up front preparation – The Archetypal Paul Feb 19 '13 at 20:55
I'd still argue that the process is the same, so I'm not sure how to further help you. Good luck in that endeavor. – gparent Feb 19 '13 at 20:58

You have a very simple problem: you need to know - how long something from the cache takes to get, as seen by a customer - the cache hit percentage - the time it takes when something ISN'T in the cache.

Let's say its 0 seconds, 90% and 0.1 seconds

9 out of 10 requests take 0 seconds 1 out of 10 requests take 0.1 seconds

The bottleneck on a uniprocessor will be at 100 request/second: 90% of them will come from the cache, 10% (meaning 10) will come from the back-end, and the back end can deliver 10/second.

At 80% of that load, you'll be fine. After that, the response time will head towards the toilet, with pain to follow. Add CPUs until you have a value you're happy with, and then set the Apache limit to say "too busy, try again later".

Send me email for the details (:-))

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